Halogen containing polymers, more especially chlorine, containing polymers and still more especially polyvinyl chloride and copolymers of vinyl chloride, have attained a high degree of commercial significance and use. Polyvinyl chloride (PVC), in particular, is widely used in packaging, siding, pipe and extruded shapes. Such large scale and diverse use of the halogen containing polymers, as exemplified by PVC, is the result, at least in part, of the stabilization of such polymers against degradation caused by light and/or heat. PVC is known to degrade upon prolonged exposure to light and/or heat during processing and use with attendant darkening or change of color and loss of physical properties (e.g. tensile, flexural and impact strengths. Such degradation detracts from the usefulness of PVC and imposes restrictions on the conditions and apparatus for processing and manufacturing PVC articles. Thus, for example, the service life of a PVC article may be significantly limited, the conditions under which the PVC article is used severely restricted and the manufacturing conditions very narrow. To overcome this problem of degradation, various substances have been added to the halogen containing polymer (e.g. PVC). These substances, known as stabilizers, have included materials such as, for example, organic antimony compounds having an antimony-sulfur-carbon linkage in the molecule (e.g. antimony tris isooctylthioglycolate). Organic sulfur compounds such as, for example, thiuram sulfide, dibenzamido-diphenyl sulfide, mercaptopyridine, mercaptobenzamidazole, mercaptobenzathiazole, and thiodipropionic acid have also been added to halogen containing polymers as stabilizers and as costabilizers (i.e. in combination with other stabilizers).
Although a number of organic antimony compounds have been taught in the art as stabilizers for halogen containing polymers (e.g. PVC) they have not received wide spread commercial acceptance because of their somewhat lower effectiveness than other compounds. In particular organic antimony compounds having an antimony-sulfur-carbon linkage (e.g. antimony tris isooctylthioglycolate) have in the past not attained significant commercial use as a stabilizer for halogen containing polymers (e.g. PVC), compared to other stabilizers, because they have, among other things, exhibited storage instability, especially when stored exposed to light and/or moisture. Such instability has been pointed out by D. J. Dieckmann in U.S. Pat. No. 4,029,618 issued June 14, 1977. This instability not only reduces the stabilizing effectiveness of the organic antimony compounds having an antimony-sulfur-carbon linkage but also results in their inconsistent stabilizing performance. Where the organic antimony compound having an antimony-sulfur-carbon linkage is a liquid or is dissolved in a liquid to form a homogeneous mixture, the storage instability, especially upon exposure to light and/or moisture, is manifested by the formation of a precipitate (i.e. insoluble solid). This formation of a precipitate is undesirable.
The organic antimony stabilizer compositions of this invention, which are useful for stabilizing halogen containing organic polymers (e.g. polyvinyl chloride) against degradation caused by heat and/or light during processing and use, are highly resistant to degradation during storage, especially during storage with exposure to light and/or moisture. Thus, the organic antimony stabilizer compositions according to this invention are highly resistant to formation of a precipitate during storage, especially storage with exposure to light and/or moisture.
It is, therefore, an object of this invention to provide an organic antimony stabilizer composition, having improved storage stability, for stabilizing halogen containing polymers. A further object of this invention is to provide a polymer composition resistant to heat and/or light comprising a halogen containing polymer and an organic antimony stabilizer composition having improved storage stability. A still further object of this invention is to provide a method for stabilizing a halogen containing polymer against heat and/or light comprising the step of adding to the halogen containing polymer an organic antimony stabilizer composition having improved storage stability. These and other objects, as will become apparent from the following disclosure, are attained by this invention.